1. Field of the Invention
The present invention relates to a flow rate switching device capable of switching a liquid flow rate in multi stages. More particularly, the present invention relates to a multi-stage type flow rate switching device capable of switching the flow rate of a liquid medicine in several stages by using a three-way stopcock.
The multi-stage type flow rate switching device according to the present invention is preferably used by being connected to a ballooned liquid medicine continuous injector (an injector where liquid medicine is filled in a balloon made of an elastic rubber material and liquid medicine is continuously injected over a period of many hours into blood vessels or the like by utilizing the force produced by contraction of the balloon as disclosed in, for example, Japanese Examined Patent Publication No. JP-B-6-83725) that is used as a means for continuously administering a liquid analgetic, anesthetic, antibiotic, or carcinostatic agent into blood vessels, hypodermic portions, epidural portions or the like in a small amount.
2. Description of Related Art
A three-way stopcock has conventionally been used in the medical field when a blood transfusion or a solution transfusion is carried out.
A three-way stopcock is typically constituted by a cylindrical portion having three branch tubes projecting in a T-like shape at the outer periphery of the cylindrical portion, a plug portion inserted in and rotatably attached to the cylindrical portion and having a liquid path in a T-like shape corresponding to the branch tubes of the cylindrical portion, and a lever attached to the plug portion for switching the flow paths.
Meanwhile, with respect to a variable small flow rate control device used in a ballooned liquid medicine continuous injector, a device comprising flow rate control tubes connected to a multi-way stopcock has already been proposed (Japanese Unexamined Patent Publication No. JP-A-5-84310). The device is constituted by a main body having a cylindrical valve chamber where one flow inlet port and at least three flow outlet ports are formed. A plug having a cylindrical valve portion is rotatably inserted into the valve chamber of the main body. A slit opened in a fan-like shape and slender holes in a straight tube shape extending opposedly in the radial direction from the base of the slit are formed in the valve portion and, even if the slender holes of the valve portion are connected to any of the flow outlet ports, the slit is connected to the flow inlet port.
However, according to the above-described flow rate control device, one flow rate control tube is necessary for each flow outlet port and various sizes of the flow rate control tubes are necessary. It is troublesome in view of production control and assembly operation to fabricate various sizes of flow rate control tubes and integrate them simultaneously. Also, the use thereof involves a drawback where the switch angle of the lever is decreased for a large number of switchings and the display is complicated whereby erroneous operation is liable to occur.
The present invention has been achieved as a result of an intensive study in view of the above-described situation and it is an object of the present invention to provide a multi-stage type flow rate switching device which simplifies switching of flow paths and rarely causes erroneous operation.